In my controller:
------------------
          while($file = readdir($dir)) {
            if($file != '.' && $file != '..' && !is_dir($dirname.$file) && $file != 'admin') {

               $page_file_arr[]=$file;
          }
 $this->template->content->set('page_file_arr',$page_file_arr);

In my view
--------------------

foreach ($page_file_arr as $page_file){
    $selection[] = array ($page_file => $page_file);
}
$page_file_arr[]=$file;

<?php  echo Form::select('selected_page',$selection,'standard',array('onclick' => 'load_file();'));?>

The output in HTML
---------------------

<select name="selected_page" onclick="load_file();">
<optgroup label="0">
<option value="biographie.php">biographie.php</option>
</optgroup>
<optgroup label="1">
<option value="galerie.php">galerie.php</option>

>>>I would like the output without <optgroup> ^^ I never requested this :)